linux-kernel - Re: [PATCH v13 10/14] unwind: Clear unwind

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20250715180105.2a36560a@batman.local.home>
Date: Tue, 15 Jul 2025 18:01:05 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org, x86@...nel.org,
 Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
 Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>, Namhyung Kim
 <namhyung@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Andrii
 Nakryiko <andrii@...nel.org>, Indu Bhagat <indu.bhagat@...cle.com>, "Jose
 E. Marchesi" <jemarch@....org>, Beau Belgrave <beaub@...ux.microsoft.com>,
 Jens Remus <jremus@...ux.ibm.com>, Linus Torvalds
 <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>,
 Jens Axboe <axboe@...nel.dk>, Florian Weimer <fweimer@...hat.com>, Sam
 James <sam@...too.org>
Subject: Re: [PATCH v13 10/14] unwind: Clear unwind_mask on exit back to
 user space

On Tue, 15 Jul 2025 12:29:12 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> The below is the last four patches rolled into one. Not been near a
> compiler.

And it shows ;-)

> @@ -117,13 +138,13 @@ static void unwind_deferred_task_work(st
>  	struct unwind_task_info *info = container_of(head, struct unwind_task_info, work);
>  	struct unwind_stacktrace trace;
>  	struct unwind_work *work;
> +	unsigned long bits;
>  	u64 cookie;
>  
> -	if (WARN_ON_ONCE(!info->pending))
> +	if (WARN_ON_ONCE(!unwind_pending(info)))
>  		return;
>  
> -	/* Allow work to come in again */
> -	WRITE_ONCE(info->pending, 0);
> +	bits = atomic_long_fetch_andnot(UNWIND_PENDING, &info->unwind_mask);

I may need to do what other parts of the kernel has done and turn the
above into:

	bits = atomic_long_fetch_andnot(UNWIND_PENDING, (atomic_long_t *)&info->unwind_mask);

As there's other bit manipulations that atomic_long does not take care
of and it's making the code more confusing. When I looked to see how
other users of atomic_long_andnot() did things, most just typecasted
the value to use that function :-/

-- Steve

>  
>  	/*
>  	 * From here on out, the callback must always be called, even if it's
> @@ -136,9 +157,11 @@ static void unwind_deferred_task_work(st
>  
>  	cookie = info->id.id;
>  
> -	guard(mutex)(&callback_mutex);
> -	list_for_each_entry(work, &callbacks, list) {
> -		work->func(work, &trace, cookie);
> +	guard(srcu_lite)(&unwind_srcu);
> +	list_for_each_entry_srcu(work, &callbacks, list,
> +				 srcu_read_lock_held(&unwind_srcu)) {
> +		if (test_bit(work->bit, &bits))
> +			work->func(work, &trace, cookie);
>  	}
>  }
>  
> @@ -162,7 +185,7 @@ static void unwind_deferred_task_work(st
>   * because it has already been previously called for the same entry context,
>   * it will be called again with the same stack trace and cookie.
>   *
> - * Return: 1 if the the callback was already queued.
> + * Return: 1 if the callback was already queued.
>   *         0 if the callback successfully was queued.
>   *         Negative if there's an error.
>   *         @cookie holds the cookie of the first request by any user